1. Field of the Invention
The present invention relates to a friction damper, and more particularly to a friction damper suitable for imparting an appropriate brake to an accelerator pedal, a brake pedal, a clutch pedal, or the like of a vehicle and a pedal device having the friction damper.
2. Description of the Related Art
Pedal devices, including an accelerator pedal, a brake pedal, a clutch pedal, and the like of a vehicle, are each comprised of a pedal disposed at an upper-limit position at which the pedal can be pressed down as well as an urging means consisting of a coil spring for urging the pedal in a direction in which the pedal returns to its upper-limit position when the pedal was pressed down.
In the case of the pedal device including an accelerator pedal, for example, as the accelerator pedal is pressed down, a throttle is opened or closed in the case of a gasoline engine, and a fuel injector is actuated in the case of a diesel engine. Conventionally, to open or close the throttle or actuate the fuel injector, the accelerator pedal and the throttle or the accelerator pedal and the fuel injector are linked together by an accelerator wire cable, and the accelerator pedal is adapted to pull the accelerator wire cable as it is pressed down.
Accordingly, when the accelerator pedal is pressed down, a reaction force (resisting force) of a value in which the resilient reaction force of the coil spring and the tensile reaction force of the accelerator wire cable are added together is applied to the accelerator pedal.
Meanwhile, fine control of fuel injection for the automotive engine is required for the purposes of low fuel consumption of vehicles and reduction of carbon dioxide, and electronic control of fuel injection such as the regulation of the throttle valve opening based on the pressing down of the accelerator pedal has been put to practical use.
In vehicles in which fuel injection of the engine is effected by electronic control, the accelerator wire cable arranged between the accelerator pedal and the throttle valve is normally omitted. With the vehicles without the accelerator wire cables, however, the reaction force with respect to the pedal pressing force differs in comparison with vehicles with the accelerator wire cables, and if a general driver who is accustomed to driving a vehicle with the accelerator wire cable drives the vehicle without the accelerator wire cable, there is a possibility of excessively pressing down on the accelerator, thereby consuming fuel more than before.
To obtain a large reaction force with respect to the pedal pressing force, if the spring force of a return spring for returning the pedal arm to the initial position of rotation is simply made large, there is a possibility of causing early fatigue to the pedal pressing foot due to the large reaction force from the return spring during constant traveling.
As a countermeasure for overcoming this problem, an arrangement has been proposed in which the pedal arm is linked to one end of a dummy cable passed through a fixed helical pipe, the other end of the dummy cable being terminated via a coil spring, to ensure that a reaction force exhibiting a hysteresis characteristic with respect to the pedal pressing force, which is similar to the conventional case in which the accelerator wire cable is provided, can be obtained by the dummy cable. However, since this countermeasure using the dummy cable requires a relatively large space for installing the dummy cable, this countermeasure can be adopted only in vehicles of large vehicle types, such as trucks and RVs, in which there is sufficient leeway in space. In addition, since various factors are involved, the adjustment of reaction force by using the dummy cable is relatively difficult, and there is a possibility of increasing the cost in order to set the reaction force to a desired value. Furthermore, although, in order to obtain the hysteresis characteristic, a metallic dummy cable is allowed to slide within the inner surface of a resin sheathing of the pipe so as to produce sliding resistance between the metallic dummy cable and the inner surface of the resin sheathing of the pipe, there is a possibility that a large change in the characteristic can occur due to the wear caused by this sliding over a long period of use.
The above-described problem occurs not only in the accelerator pedals, but can also occur in cases where appropriate rotational resistance is produced by using the above-described dummy cable or the like in brake pedals or clutch pedals, for example.